Plasma Treatment for Sandwich Panels
Plastic sandwich panels with a honeycomb core are characterized by high strength and low weight per unit area. This is why they are commonly used in utility vehicles, the aerospace and aircraft industries, and in building construction. Both the outer cladding and the honeycomb core of these panels are being manufactured increasingly from nonpolar resins such as PP. However, these resins have a relatively low surface energy and can be painted or glued only after a pretreatment.
Traditional pretreatment techniques such as flaming, corona treatment or application of a primer are often associated with considerable expense and environmental impact. Compared to these approaches, treating the surface of such panels with an atmospheric plasma offers a number of processing benefits. The surface treatment takes place in-line, since the plasma treatment can be incorporated directly into the panel production process. Using specially developed rotary nozzles, processing speeds of up to 25 m/min over a working width of 3 m can be achieved. An additional advantage is that the temperatures of the plastic surface during the plasma treatment usually are below 20°C.
The plasma can actually perform two different tasks during panel production: first of all, the cladding layer can be treated in order to prepare the surface for application of paint; secondly, the honeycomb structures can also undergo plasma treatment as a means of improving adhesion to the glued cladding. In this way, the plasma treatment also enables use of recycled plastic or wood-plastic composite (WPC) as the core – because of the difficult to bond surfaces, this was previously not possible.
Investigations aimed at ensuring the quality of surface treatment by means of plasma are currently being conducted at the Institute for Plastics Processing (IKV). These have demonstrated that with optical emission spectroscopy (OES) online process monitoring during the plasma treatment can be achieved. OES is easy to use, robust and economical, and is thus ideally suited for industrial use.